This project is designed to understand the role of hormones and growth factors in normal mammary gland development and differentiation. We wish to understand how milk-protein production is controlled by various hormones. Studies include: 1) examination of the role of thyroid hormones, adrenal steroids and Vitamin D in synthesis and secretion of milk proteins in organ culture, 2) examination of the role of epidermal growth factor and mammary gland-derived growth factors in lobulo-alveolar development of the immature mouse mammary gland, 3) defining the roles of estrogen and progesterone in priming the mammary tissue prior to whole organ culture to determine their effects on induction of EGF receptors, mammary gland-derived growth factor receptors and the production of growth factors by the animals.